Warp speed space travel and GR:

[paddoboy]

The reason I reposted that portion of Prof. Lewis' comment, in the post above, is because it speaks directly about the issue. GR is not a theory of fundamental cause and effect. It is a descriptive field theory that describes only the effect. It does not say anything about the why or how, matter tells space-time or other matter how to move, it only describes the result. I have had a long standing disagreement with Brucep on this point, where I have referred to his interpretation as a modern interpretation. A view that does think of space-time as a thing.

I am not sure I agree entirely with Prof. Lewis as he describes space-time in that last sentence,

We also while being able to explain that the Universe evolved from the BB, likewise we do not know the why or how.
Also whether the view of whether spacetime is real or just purely a mathematical background against which the equations of GR are solved is in my opinion debatable.
Do you accept that space is real? Do you accept that time is real?
I see all as non physical reality, and as long as one does not excessively attribute the suppositions as mentioned by Professor Lewis thus, "The mistake people make is to treat space-time as a thing and then make suppositions of what happens in relativity based on this". I see no barrier to accepting spacetime as a non physical reality that has been observed to be warped, twisted and rippled [gravity waves] in the presence of mass/energy.

 

[paddoboy]

http://www.quora.com/Is-spacetime-a-real-thing-or-just-a-mere-concept

"If yes, you should consider spacetime to be a real "thing" as well. Spacetime is not just a passive arena for light and matter. It has its own dynamics; it interacts" ...




http://einstein.stanford.edu/content/relativity/q411.html

 

[tashja]

Thanks Tashja, I was hoping you would do that.

You're welcome, sweet. I sent your follow-up question to Prof. Lewis, who I publicly want to thank for his continued contribution to our forum. I know he's following this thread, so..

Prof. Lewis!

Thanks Tashja, I was hoping you would do that.
Using a geometrical theory about the manifold of space and time means you don't have to invoke a force or fictional force to find the path (geodesic )of a particle. I was wondering, would a force have to be invoked to explain a path in what Prof: G. Lewis is saying about 'matter tells matter how to move'.

I think the idea of putting-in a force of attraction with no explanation of how that force attracts is also a mathematical tool, and so like the spacetime model is just a model.
I'm not even a layman in these things and would find reading scientific papers a bit beyond me unless they are 'interpreted ' down to my level.
Thanks again Tashja and thank you Prof: Lewis.

Hi -


No – there’s no “force” as it is easy to see that any free-fall observer “feels” no force when they travel. The equations of relativity just tell you how to connect events, but it is just one of those things that we have to chalk up to being a property of the universe. If gravity is advanced beyond Einstein’s GR (such as in a GUT, there may be an answer to why, but at the moment, that’s it).


Cheers – Geraint


Ps – I am a big fan of people discussing science – and wish I had more time to, but I could spend all my life on forums etc, but have to actually do some science (and teaching and administration etc).


I took a look at the forum – was interested to see “"Professor GeraintLewis is fabricating fiction for science. His credentials aren't worth the paper and ink used in their forgery”” - interesting view point All I can say is that I submit my fabricated fiction to respected journals, where it is peer reviewed and published, before being discussed by community. I am happy for someone to counter my statements in the literature and I will happily debate them there Put your money where your mouth is is my operating procedure.



//\\//\\//\\//\\//\\//\\//\\// \\//\\//\

Geraint F Lewis,

Professor of Astrophysics

Sydney Institute for Astronomy
Associate Head (Research),
School of Physics A28
The University of Sydney

 

[OnlyMe]

We also while being able to explain that the Universe evolved from the BB, likewise we do not know the why or how.

You should know by now I don't get into discussions about the BB. I don't see it as different than speculating about who we are or why we are! There is no way to know who is right or wrong, or if anyone is even close to the truth...

Also whether the view of whether spacetime is real or just purely a mathematical background against which the equations of GR are solved is in my opinion debatable.

I am not even sure that even makes sense. "... just purely a mathematical background against which the equations of GR are solved..."? Solving the equations of GR is where space-time comes from. Your phrasing suggests you start with the assumption that space-time is a thing, to begin with... A preconception....

Do you accept that space is real? Do you accept that time is real?

How many debates over definitions of time have there been with no consensus? Neither of those questions mean anything, without a clear definition of just (and exactly) what you mean by space and time. Change is real. Time is what we call our experience of change. Space is more difficult because it really depends what preconceptions you begin with. Are you talking about the distances between things? Or perhaps some box that everything is in?

I see all as non physical reality,

So paddoboy, what is the difference between a non physical reality and an idea?

and as long as one does not excessively attribute the suppositions as mentioned by Professor Lewis thus, "The mistake people make is to treat space-time as a thing and then make suppositions of what happens in relativity based on this". I see no barrier to accepting spacetime as a non physical reality that has been observed to be warped, twisted and rippled [gravity waves] in the presence of mass/energy.

It seems above you at first agree with Prof. Lewis and then in the next sentence do exactly what he warned against.

Space-time does not make things happen. It is a description of the geometry of what is and how it changes, of what happens. Curve, warp, ripple and twist are words. Inaccurate attempts to translate the geometry into words.

 

[paddoboy]

So paddoboy, what is the difference between a non physical reality and an idea?
It seems above you at first agree with Prof. Lewis and then in the next sentence do exactly what he warned against.
Space-time does not make things happen. It is a description of the geometry of what is and how it changes, of what happens. Curve, warp, ripple and twist are words. Inaccurate attempts to translate the geometry into words.

Like I said, the question is debatable and I have shown that with a couple of reputable links.
Whatever else you chose to read into things is your business.

I know he's following this thread, so..

Prof. Lewis!
Ps – I am a big fan of people discussing science – and wish I had more time to, but I could spend all my life on forums etc, but have to actually do some science (and teaching and administration etc).


I took a look at the forum – was interested to see “"Professor GeraintLewis is fabricating fiction for science. His credentials aren't worth the paper and ink used in their forgery”” - interesting view point All I can say is that I submit my fabricated fiction to respected journals, where it is peer reviewed and published, before being discussed by community. I am happy for someone to counter my statements in the literature and I will happily debate them there Put your money where your mouth is is my operating procedure.



//\\//\\//\\//\\//\\//\\//\\// \\//\\//\

Geraint F Lewis,

Professor of Astrophysics

Sydney Institute for Astronomy
Associate Head (Research),
School of Physics A28
The University of Sydney

If Professor Lewis is reading this, let me just say that the poster who made the inane remarks concerning yourself, is one that I would say is on par to Zarkov, in the old ABC forum, and as such his remarks and claims need to be treated with a grain of salt.

 

[The God]

Ref Post # 45 (Pl someone tell me how do I take messages in quote as being done by others).

Since now prof Lewis is directly watching this thread, so this post is being addressed to him directly, with due thanks and regards to Tashja.

Prof Lewis,

My respect to you; Apology in advance in case I object to your views harshly. Nothing personal and nothing demeaning.

I have read your pointed paper (Francis et al 2007), my sincere complements to all four of you for being so direct and blunt, for bringing out in open the kind of misinformation being tought to young graduate students about spacetime expansion. Why this is happening ? Either the teachers are not able to figure out how to explain this or they themselves are victim of the same thing during their younger learning days and following the same misleading and confusing stuff.

You are a very courageous man, but since you are a great proponent of GR (A man working on Warp Drive cannot be otherwise) so this paper has not much affected you negatively.

But, good professor, what has been achieved by this paper ? Let us see..

You start nicely and define the objective of your paper that whatever being said about spacetime expansion is bad and misleading. Great. Then you catch hold of that metaphoric statement by John Wheeler and defensively bring in charge-charge interaction and in the same breath chuck that out by bringing in ElectroMagnetism. That appears adhoc and unconvincing. Then you bring in the cosmological picture, loosely talk about privileged frames (which is barred by SR) and pump in the concept of cosmic fluid (may be you are referring to matter) creating the same confusion which you wanted to avoid at the first place. You make a reference to cause effect, without really delving much on the cause and create further confusion by saying...distances between the points are increasing and thus the space......as you agree somewhere about something else that this is nothing but semantics, this is clear from extract taken from your below paper. This is as confusing as the original explanation by those teachers.

Extract from your paper
...............We can describe this alteration as the expansion of space, but the key point is that it is a result of the change in the mean energy density, not the other way around. The expansion of space does not cause the distance between galaxies to increase, rather this increase in distance causes space to expand, or more plainly that this increase in distance is described by the framework of expanding space. There is therefore no need to look for Newtonian analogues to the expansion of space, since it is an effect rather than a cause..........

Then you go on to say that due to the expansion of spacetime the wavelength (of light) does not stretch and try to explain the same with variable frames. I am sure majority holds the opinion (or they are tought) that it stretches, so you are admitting one more incorrect explanation.

You unequivocally state that expansion of spacetime should not be confused with material expansion, it is geometry as per GR. But Professor, any motion under any influence has to take a geometrically defined path only, a geometry per say cannot create motion, source (cause) has to be somewhere else. Point is Geometrical expansion is as confusing as what the good teachers were teaching.

The best is yet to come, you try to explain why the galaxy inners do not expand (like space between Earth and Sun). The people in general reconcile that it is due to Gravitational hold, isn't it ? In your paper you take an example of room walls and argue that they are together due to ElectroMagnetic force so the spacetime expansion does not apply, this instantly gives a question which you did not take up....What is the lower limit of this ElectroMagnetic Coupling beyond which (on the lower side) the spacetime expansion will take over ? For that matter what is the lower limit of Gravitational hold (or what is the lower limit of distortion of spacetime) beyond which expansion would take place ? You pump in DE also, the DE component is much much higher than the Baryonic ElectroMagnetism, so I am sure DE should demonstrate itself everywhere....Unless and untill you are trying to say that spacetime which is flat without Gravitational Distortion is a good candidate for expansion...you try to bring in locality but then this will make expansion Hubble Free.

Finally a question which I am sure all the students who are tought incorrectly should ask.....Take a normal room of 4 X 4 X 4 meters at t = 0, the walls of this room are flexible and they can be expanded keeping the shape as cube even while expanding. There is an observer at the center of the cube body but the problem is that this observer cannot see beyond 1 meter, so he can only see a sub set (Sphere of 1 Meter) of room. There are two observable dots also on a radial line one at x = 0.2 meter from center and another at t = 0.4 meter. Now this room walls are expanding because few funny guys unknown to observer are pulling it from outside. How would the observer with restricted viewing capacity know that universe is expanding ? Without any reference to material.

(We are like that observer only, our observable universe is the sub set of full universe, although our observation range is increasing day by day, but it cannot be said that we have seen the edge.)

 

[OnlyMe]

Ref Post # 45 (Pl someone tell me how do I take messages in quote as being done by others).

[qu ote] enclose the quoted portion inside the leadin quote and ending /quote, with brackets and without the spaces I inserted here. [/qu ote]
It then looks like this,

enclose the quoted portion inside the leadin quote and ending /quote, without the the spaces I inserted here.

[qu ote=some name] to quote someone by name, enclose the quoted portion inside the leadin quote and ending /quote, without the the spaces I inserted here. [/qu ote]

It then looks like this,

to quote someone by name, enclose the quoted portion inside the leadin quote and ending /quote, without the the spaces I inserted here.

In the current forum software things that are quoted by one poster do not appear in the post quote when you use the REPLY button at the bottom of a post. I placed the above quote inside [in dent] without the spaces [/in dent], to INDENT them and make them stand out, in this post.

Since now prof Lewis is directly watching this thread, so this post is being addressed to him directly, with due thanks and regards to Tashja.

Prof Lewis,

My respect to you; Apology in advance in case I object to your views harshly. Nothing personal and nothing demeaning.

I have read your pointed paper (Francis et al 2007),

I guess now I will have to make time sooner rather than later to read the professor's paper. I don't always agree with what I have seen of his work, but, much if not all, of your response seems over the top... Meaning more emotional than reasoned...

The further into the universe we look and attempt to explain what we find, the greater our attempts to explain become speculation. That is the nature of any attempt to understand things beyond our abitilty to (figuratively) reach out and touch it. Keeping that in mind and without you providing any corrective interpretation/speculation, of your own about the work you criticize, it seems to me your response is more emotional than reasoned.

 

[danshawen]

The further into the universe we look and attempt to explain what we find, the greater our attempts to explain become speculation.

You were right again, OnlyMe and also brucep gets an honorable mention. Exotic matter was actually discovered at the LHC in 2014. Thanks.

If you will all excuse me for a little while, I have a few hats and some raw crow I need to eat. Maybe a few dozen apology letters to Kip Thorne are also in order.

I was wrong; not the first time, by a long shot. I'm here to learn of course. Some of us have more to learn than others.

 

[sweetpea]

You're welcome, sweet. I sent your follow-up question to Prof. Lewis,

Thanks Tashja. I can see the Prof: is busy and so I won't be derecting anything his way...Hint, hint Tashja, I think he was politely asking not to be disturbed.
That's my take. Thanks again

 

[sweetpea]

I might restate is as.., it does not matter whether you imagine that by some means matter exerts some force that curves space-time or that space-time is just a geometric field description of how one massive object affects the motion of another massive object....., ]in either case there is some force at play.., either directly between the two massive objects or by each massive object affecting its local geometry of space-time.., which then affects the other massive object....

Your assuming it is a 'force' which goes on to effect spacetime.
Why mass and energy effect spacetime is unknown (you know that).

In a geometrical theory about the manifold of space time, it is taken as a 'given' that mass and energy do alter spacetime. Using the geometrical spacetime equations will tell you how much spacetime has been affected. Note: that is not 'why' it has been affected.

In a Newtonian picture you may see a planet accelerate about the sun, and so in that picture you assume a force is at work.
In a geometrical spacetime picture the spacetime has been affected by the mass and energy of the sun. The planet is just following an inertial path (geodesic) through this altered spacetime.
Spacetime is altered more nearer the sun than further out, this will give the appearance,Note: just an appearance, of a 'force' at work causing the planet to accelerate or decelerate.

 

[tashja]

Since now prof Lewis is directly watching this thread, so this post is being addressed to him directly, with due thanks and regards to Tashja.

Hi God,

I thought your post was/is a very interesting critique of the paper. You raised a few issues that I'm sure many of us have pondered at some point. Below is Prof. Lewis's reply. If you have any more questions/comments, just ask. I can't guarantee you that all of them will be answered to your satisfaction (or be answered at all), but I'll make sure they get there.

Ref Post # 45 (Pl someone tell me how do I take messages in quote as being done by others).

Since now prof Lewis is directly watching this thread, so this post is being addressed to him directly, with due thanks and regards to Tashja.

Prof Lewis,

My respect to you; Apology in advance in case I object to your views harshly. Nothing personal and nothing demeaning.

I have read your pointed paper (Francis et al 2007), my sincere complements to all four of you for being so direct and blunt, for bringing out in open the kind of misinformation being tought to young graduate students about spacetime expansion. Why this is happening ? Either the teachers are not able to figure out how to explain this or they themselves are victim of the same thing during their younger learning days and following the same misleading and confusing stuff.

You are a very courageous man, but since you are a great proponent of GR (A man working on Warp Drive cannot be otherwise) so this paper has not much affected you negatively.

But, good professor, what has been achieved by this paper ? Let us see..

You start nicely and define the objective of your paper that whatever being said about spacetime expansion is bad and misleading. Great. Then you catch hold of that metaphoric statement by John Wheeler and defensively bring in charge-charge interaction and in the same breath chuck that out by bringing in ElectroMagnetism. That appears adhoc and unconvincing. Then you bring in the cosmological picture, loosely talk about privileged frames (which is barred by SR) and pump in the concept of cosmic fluid (may be you are referring to matter) creating the same confusion which you wanted to avoid at the first place. You make a reference to cause effect, without really delving much on the cause and create further confusion by saying...distances between the points are increasing and thus the space......as you agree somewhere about something else that this is nothing but semantics, this is clear from extract taken from your below paper. This is as confusing as the original explanation by those teachers.

Extract from your paper
...............We can describe this alteration as the expansion of space, but the key point is that it is a result of the change in the mean energy density, not the other way around. The expansion of space does not cause the distance between galaxies to increase, rather this increase in distance causes space to expand, or more plainly that this increase in distance is described by the framework of expanding space. There is therefore no need to look for Newtonian analogues to the expansion of space, since it is an effect rather than a cause..........

Then you go on to say that due to the expansion of spacetime the wavelength (of light) does not stretch and try to explain the same with variable frames. I am sure majority holds the opinion (or they are tought) that it stretches, so you are admitting one more incorrect explanation.

You unequivocally state that expansion of spacetime should not be confused with material expansion, it is geometry as per GR. But Professor, any motion under any influence has to take a geometrically defined path only, a geometry per say cannot create motion, source (cause) has to be somewhere else. Point is Geometrical expansion is as confusing as what the good teachers were teaching.

The best is yet to come, you try to explain why the galaxy inners do not expand (like space between Earth and Sun). The people in general reconcile that it is due to Gravitational hold, isn't it ? In your paper you take an example of room walls and argue that they are together due to ElectroMagnetic force so the spacetime expansion does not apply, this instantly gives a question which you did not take up....What is the lower limit of this ElectroMagnetic Coupling beyond which (on the lower side) the spacetime expansion will take over ? For that matter what is the lower limit of Gravitational hold (or what is the lower limit of distortion of spacetime) beyond which expansion would take place ? You pump in DE also, the DE component is much much higher than the Baryonic ElectroMagnetism, so I am sure DE should demonstrate itself everywhere....Unless and untill you are trying to say that spacetime which is flat without Gravitational Distortion is a good candidate for expansion...you try to bring in locality but then this will make expansion Hubble Free.

Finally a question which I am sure all the students who are tought incorrectly should ask.....Take a normal room of 4 X 4 X 4 meters at t = 0, the walls of this room are flexible and they can be expanded keeping the shape as cube even while expanding. There is an observer at the center of the cube body but the problem is that this observer cannot see beyond 1 meter, so he can only see a sub set (Sphere of 1 Meter) of room. There are two observable dots also on a radial line one at x = 0.2 meter from center and another at t = 0.4 meter. Now this room walls are expanding because few funny guys unknown to observer are pulling it from outside. How would the observer with restricted viewing capacity know that universe is expanding ? Without any reference to material.

(We are like that observer only, our observable universe is the sub set of full universe, although our observation range is increasing day by day, but it cannot be said that we have seen the edge.)

Hi Tashja -


I’ve not had a chance to chat with “The God” before, but please excuse if the following sounds a little terse – must get some sleep before tomorrow’s meetings -

There are a few issues raised in the post, and I’ll try to cover as much as possible, but if I miss anything out, it’s only because I missed them.

So, some things – Francis et al – three of the authors where grad students at the time of writing. We spent a lot of time understanding the meaning of relativity for that paper, and there have been several follow up papers on the topic. The paper is not meant to be definitive (no science is) but the level is above popular science, so I guess I must apologise if the language grates a little.

Bu the key point is that there is a lot of misunderstanding when it comes to relativity – as an example, photons simply don’t stretch with the universe. Photons don’t carry information, including their wavelength, and so this cannot stretch as the universe expands. In fact, the only thing that really matters is the frame of the emitter and the observer, and GR carries the photon from one from the other. In special relativity, when a photon is observed to be blue shifted, where does the squeezing occur? At emission, during flight, or when entering the eye? None of these, really, as it is a frame dependent quantity.

I have to head off now, but the question of what “observable dots” (what ever they are) do – they respond to the rest of the mass in the universe – as we expect -


http://adsabs.harvard.edu/abs/2006MNRAS.373..382B


Cheers - Geraint


//\\//\\//\\//\\//\\//\\//\\//

Geraint F Lewis,

Professor of Astrophysics

Sydney Institute for Astronomy
Associate Head (Research),
School of Physics A28
The University of Sydney

 

[paddoboy]

Hi God,

I thought your post was/is a very interesting critique of the paper. You raised a few issues than I'm sure many of us have pondered at some point. Below is Prof. Lewis's reply. If you have any more questions/comments, just ask. I can't guarantee you that all of them will be answered to your satisfaction (or be answered at all), but I'll make sure they get there.

Great job again tashja. You seem to have all these Professors at your beck and call.
You are now an invaluable source for this forum.

 

[paddoboy]

I have read your pointed paper (Francis et al 2007), my sincere complements to all four of you for being so direct and blunt, for bringing out in open the kind of misinformation being tought to young graduate students about spacetime expansion. Why this is happening ? Either the teachers are not able to figure out how to explain this or they themselves are victim of the same thing during their younger learning days and following the same misleading and confusing stuff.

What are your credentials to be able to claim the nonsense you have?

You are a very courageous man, but since you are a great proponent of GR (A man working on Warp Drive cannot be otherwise) so this paper has not much affected you negatively.

I wasn't aware the Prof was working on any warp drive mechanism. He obvious was simply making possible speculative assumptions, based on what is allowed by the laws of physics and GR.

But, good professor, what has been achieved by this paper ? Let us see..

You seem rather childishly dismissive...why is that?

You start nicely and define the objective of your paper that whatever being said about spacetime expansion is bad and misleading. Great. Then you catch hold of that metaphoric statement by John Wheeler and defensively bring in charge-charge interaction and in the same breath chuck that out by bringing in ElectroMagnetism. That appears adhoc and unconvincing.

All I see is a view on how the presently accepted interpretation of spacetime, maybe misleading.

Then you go on to say that due to the expansion of spacetime the wavelength (of light) does not stretch and try to explain the same with variable frames. I am sure majority holds the opinion (or they are tought) that it stretches, so you are admitting one more incorrect explanation.

That did surprise me at first read, then when he explained re blueshift, I immediatley saw the point he was making.

You unequivocally state that expansion of spacetime should not be confused with material expansion, it is geometry as per GR.

I simply saw that as an interpretation, to try and avoid the confusion that sometimes is generated and of which he spoke.
There is also another rather limited interpretation that is sometimes [although rarely used] called "shrinking rulers"

The best is yet to come, you try to explain why the galaxy inners do not expand (like space between Earth and Sun). The people in general reconcile that it is due to Gravitational hold, isn't it ? In your paper you take an example of room walls and argue that they are together due to ElectroMagnetic force so the spacetime expansion does not apply, this instantly gives a question which you did not take up....What is the lower limit of this ElectroMagnetic Coupling beyond which (on the lower side) the spacetime expansion will take over ? For that matter what is the lower limit of Gravitational hold (or what is the lower limit of distortion of spacetime) beyond which expansion would take place ? You pump in DE also, the DE component is much much higher than the Baryonic ElectroMagnetism, so I am sure DE should demonstrate itself everywhere...

You seem rather confused.
Let me explain to the best of my ability.....any body in any room, on any planet, in any galaxy, in any group of galaxies, is first and foremost decoupled from the overall expansion rate by gravity, then as we move down to smaller and smaller details, we find the EMF, the strong and weak nuclear forces coming into their own.
Not too hard to understand even for a lay person such as myself.

Finally a question which I am sure all the students who are tought incorrectly should ask.....

Wow! and the childish dismissive nonsense continues.

Take a normal room of 4 X 4 X 4 meters at t = 0, the walls of this room are flexible and they can be expanded keeping the shape as cube even while expanding. There is an observer at the center of the cube body but the problem is that this observer cannot see beyond 1 meter, so he can only see a sub set (Sphere of 1 Meter) of room. There are two observable dots also on a radial line one at x = 0.2 meter from center and another at t = 0.4 meter. Now this room walls are expanding because few funny guys unknown to observer are pulling it from outside. How would the observer with restricted viewing capacity know that universe is expanding ? Without any reference to material.

(We are like that observer only, our observable universe is the sub set of full universe, although our observation range is increasing day by day, but it cannot be said that we have seen the edge.)

Not 100% sure what you are asking here, but anyway I'll have my usual shot at answering it the way I see things.
The further we look into the Universe/spacetime, the faster the expansion of spacetime. In fact at specific distances, galaxies are receding [due to spacetime expansion at and even in excess of "c".
Therefor light from these regions will never reach us.
Note: Spacetime [massless] is not curtailed by the universal speed law of light.
The other point is that in the very distant future, the galaxies we see now that are not gravitationally bound to our own group, will have receded beyond our viewable range due to the intervening expansion of spacetime.
All that will be viewable will be our local group which would be then merged into one larger galaxy.

If Prof Lewis sees any mistakes or errors in my interpretation in trying to alleviate your confusion, then I would appreciate him to correct.

To the God, my apologies if I have not seemed to be as friendly and respectful as the Prof and tashja in her address to you, but sometimes I can be a cranky old bastard, especially when nobody's show the disrespect and dismissive attitude you have.

To Prof Lewis, I do have a couple of questions re your paper and when I satisfy myself as to how best to put those questions, I'll certainly list them for your perusal and comment.
Again thanks for your time and effort [as well as tashja] and my apologies for the rather disrespectful sham of a post from God, which you handled with great aplomb.

 

[OnlyMe]

Your assuming it is a 'force' which goes on to effect spacetime.
Why mass and energy effect spacetime is unknown (you know that).

In a geometrical theory about the manifold of space time, it is taken as a 'given' that mass and energy do alter spacetime....

Mass and energy are used to determine what the geometry of space-time is, but they do not create space-time, as even a quasi-independent thing... Back to my earlier quote of Prof. Lewis, from tashja's post.

The concept of space-time is not banished – you just have to realise what it is – the mathematical medium that tells you how mass and energy influences mass and energy. Relativity tells you how to connect events with particles and photons, and this depends upon the mass and energy distribution around it.

The mistake people make is to treat space-time as a thing and then make suppositions of what happens in relativity based on this.

Very often in popular texts descriptions of space-time come across as if it were a thing, that makes objects and photons move in a particular way. I refer to that often as, a (or the) modern interpretation. The only thing that we know with any certainty about GR and the space-time model of gravitation is that it accurately describes what we observe......., and that it doesn't say anything certain about why or how what we observe is as it is.

Most of the time when I comment about these issues, it is from some middle ground between GR and QM... That is not where I began, it is where I am. And no I don't have a GUT.., and GR and QM have not been made to play nice.., yet. However, we have spent a hundred years with GR and are no closer to the how and why. It would be unwise to discard other possibilities out of hand.

If the discussion is limited to GR, then there is no force but there is also, no why or how. We can accept that gravitation exists as an a priori. We Can even assert with confidence that gravitational fields are well described by GR, because experience supports this... But it is not an a priori, or acceptable given fact that space-time is a thing or that because as a field description it is successful, there is no force at play... Not if the objective is to one day understand the fundamental mechanism, that leads to what we understand as gravitation.

 

[paddoboy]

. Not if the objective is to one day understand the fundamental mechanism, that leads to what we understand as gravitation.

Agreed, and that also applies to the why and how of the BB.
A future QGT??

 

[OnlyMe]

Agreed, and that also applies to the why and how of the BB.
A future QGT??

I think that quote was from my post immediately above!

But I don't think that a search for a better understanding of the fundamental origins of gravitation and inertia and creation speculations centering on the Big Bang are anywhere near the same. Though at least to begin the fundamentals of the how and why of gravity and inertia are speculative, there is some possibility that answers may one day be found. The truth of the Big Bang and variations will remain speculation to the end of time, since the answers lie so far in the past they cannot be tested and confirmed.

So you have finally drug something on the BB out of me!

 

[danshawen]

Agreed, and that also applies to the why and how of the BB.
A future QGT??

Yes indeed. Wow.

 

[paddoboy]

​

I think that quote was from my post immediately above!

? I hadn't really noticed in actual fact.

But I don't think that a search for a better understanding of the fundamental origins of gravitation and inertia and creation speculations centering on the Big Bang are anywhere near the same. Though at least to begin the fundamentals of the how and why of gravity and inertia are speculative, there is some possibility that answers may one day be found. The truth of the Big Bang and variations will remain speculation to the end of time, since the answers lie so far in the past they cannot be tested and confirmed.

You don't believe that knowing the the how and why of the BB, [at least in part] which was afterall the evolution of space and time as we know them, would not in turn lead to the true nature of gravity, which exhibits itself from that same spacetime?
I certainly see a connection there.

So you have finally drug something on the BB out of me!

Didn't set out to do that, I just see a connection.
Afterall space and time [spacetime] were the first to evolve from the BB....the rest came later.

 

[tashja]

Mass and energy are used to determine what the geometry of space-time is, but they do not create space-time, as even a quasi-independent thing... Back to my earlier quote of Prof. Lewis, from tashja's post.

Very often in popular texts descriptions of space-time come across as if it were a thing, that makes objects and photons move in a particular way.

It might yet be a thing, Only. Maybe not in classical GR, but in a quantum theory of gravity. I recall AlphaNumeric saying something about spacetime being made out of gravitons:

If you were to cling to the quantum field theory notation that a field is actually the large scale effect of lots of particles then space-time is not a place where particles are, it is particles.

For instance, Maxwell (and a few people after him) realised you can write electromagnetism in terms of a 4-potential $$A_{\mu}$$. We now view this $$A_{\mu}$$ as the vector field associated to the photon particle. Likewise for fields for the strong and weak forces. In general relativity there's the field $$g_{\mu\nu}$$ which defines the metric. If this were to be quantised then you would have it being the large scale appearance of graviton particles.

This is precisely what happens in string theory. When you compute massless closed string modes you find a set of modes which take on all the properties of $$g_{\mu\nu}$$. The graviton is a large scale effect of string oscillations, just like all other particles. This would mean that space-time is actually some kind of seething mass of strings. This isn't an isolated concept either. The branes of string theory are often thought of as somehow 'solid' objects unto themselves but infact they should be viewed on a quantised level as massive tachyon condensates, formed of a huge number of strings in a single coherent state. Space-time is just a particular case of this, as there are examples of 'space filling branes'. Loop quantum gravity takes a similar approach but it uses spin foam networks and tries to start from them and build up. It's had considerably less success.

 

[paddoboy]

It might yet be a thing, Only. Maybe not in classical GR, but in a quantum theory of gravity. I recall AlphaNumeric saying something about spacetime being made out of gravitons:

I have given a few links that look on spacetime as real. Just as we may believe we are not alone in the Universe, although the true answer is we do not know, I see a similar situation with spacetime and space and time. There are for's and against's, and appears to still be rather a debatable point.